Noobie help, upgrading graphics card

Hey guys, so I'm probably going to get laughed at for my system. I have an old Vaio that I'm putting a new card into. Here are my computer's specs:

http://www.dealtime.com/xPF-Sony-VAIO-Digital-Studio-PC...

So basically it has a P4 2.4 with 2gb RAM (can't remember the speed), I've upgraded the hard drives, threw in a 128mb 9800 Pro AGP and that's about it. I recently bought a new monitor that runs 1920x1200 and have bought a 256mb X1950 Pro. What kind of bottlenecking can I expect with the X1950 Pro since my system is so old? My 9800 Pro has run CS:S pretty well and that's about all I play. I don't play games that often, so that's why haven't had the need to get a new computer.

Another thing is my PS only has a DC output of 270W max. Should I replace the PS with a new one or could I just run a second PS, put it on top of the desktop and just run the power cable to the card? I'm not sure how to go about replacing the PS since it's a Sony and it takes a certain kind that locks into the inside of the computer.

Does Frys sell the 4 pin molex to 6 pin PCI-E power cable adapter needed to power the card?

TIA for any help  

Here's my PS's specs:

Output-
+5v 25A max
+3.3v 13A max
+12v 15A max
-12v 0.2A max
+12vsp 1.2A max
AUX +5vb 1.8A max

+12, +12vsp total 180W max
+5, +3.3v total 146.3W max
DC output total 268.9W max

EDIT: Well, I took a closer look at the PSU and saw that there's an attachment that the PSU slides into. So, I guess I'll be looking for a new PSU.

Now from what I've read, I should get one that's >400W and has at least 30 amps on the +12v rail. My question is, does the 30 amps need to be on one rail or can I run a PSU that has (for example) +12v1 18amps and +12v2 18amps making for a total of 36amps on the +12 rails?